Speaking from experience and what I have read. I grow my plants past the typical harvest window of 8 weeks because I LOVE the couch lock stone and it KILLS migraines. In the last 6 years of my experimenting with my particular favorite plant genetics (its a purple cross with something) I have noticed that extending the length of darkness does only 1 thing...
it does absolutely nothing but extend the length of time it takes the plant to finish.
I flower for 12-16 weeks sometimes (to get SUPER couch lock weed) and on some sets of plants I have gone 14-10 and there was no speed up in ambering of pistils, or trics. The quality was not effected at all and neither was the yield. It only made the finishing of the plants longer.
This has been in my experience and with my specific plant though. I have noticed that many cannabis plants are different and react differently to certain situations so you need to feel free to experiment on your own, that is one of the most fun parts of growing! Experiment with LST, FIMM, Hydro and soil. Find what you like to grow with and do that. Learn what your plant likes and responds to by growing it and trying out new grow methods
Peace~